25,225 research outputs found
X-ray photometry
I describe a method for synthesizing photometric passbands for use with
current and future X-ray instruments. The method permits the standardisation of
X-ray passbands and thus X-ray photometry between different instruments and
missions. The method is illustrated by synthesizing a passband in the
XMM-Newton EPIC pn which is similar to the ROSAT PSPC 0.5-2 keV band.Comment: Accepted for publication in MNRA
Shock-induced separation of adiabatic turbulent boundary layers in supersonic axially symmetric internal flow
An experimental investigation at Mach 4 of shock-induced turbulent boundary layer separation at the walls of axially symmetric flow passages is discussed, with particular emphasis placed on determining the shock strengths required for incipient separation. The shock waves were produced by interchangeable sting-mounted cones placed on the axes of the flow passages and aligned with the freestream flow. The interactions under study simulate those encountered in axially symmetric engine inlets of supersonic aircraft. Knowledges of the shock strengths required for boundary layer separation in inlets is important since for shocks of somewhat greater strength rather drastic alterations in the inlet flow field may occur
Submm-bright QSOs at z~2: signposts of co-evolution at high z
We have assembled a sample of 5 X-ray and submm-luminous z~2 QSOs which are
therefore both growing their central black holes through accretion and forming
stars copiously at a critical epoch. Hence, they are good laboratories to
investigate the co-evolution of star formation and AGN. We have performed a
preliminary analysis of the AGN and SF contributions to their UV-to-FIR SEDs,
fitting them with simple direct (disk), reprocessed (torus) and star formation
components. All three are required by the data and hence we confirm that these
objects are undergoing strong star formation in their host galaxies at rates
500-2000 Msun/y. Estimates of their covering factors are between about 30 and
90%. In the future, we will assess the dependence of these results on the
particular models used for the components and relate their observed properties
to the intrinsice of the central engine and the SF material, as well as their
relevance for AGN-galaxy coevolution.Comment: 6 pages, 2 figures, contributed talk to "Nuclei of Seyfert galaxies
and QSOs - Central engine & conditions of star formation" November 6-8, 2012.
MPIfR, Bonn, Germany. Po
X-ray absorbed QSOs and the QSO evolutionary sequence
Unexpected in the AGN unified scheme, there exists a population of broad-line
z~2 QSOs which have heavily absorbed X-ray spectra. These objects constitute
10% of the population at luminosities and redshifts characteristic of the main
producers of QSO luminosity in the Universe. Our follow up observations in the
submm show that these QSOs are often embedded in ultraluminous starburst
galaxies, unlike most QSOs at the same redshifts and luminosities. The
radically different star formation properties between the absorbed and
unabsorbed QSOs implies that the X-ray absorption is unrelated to the torus
invoked in AGN unification schemes. Instead, these results suggest that the
objects represent a transitional phase in an evolutionary sequence relating the
growth of massive black holes to the formation of galaxies. The most puzzling
question about these objects has always been the nature of the X-ray absorber.
We present our study of the X-ray absorbers based on deep (50-100ks) XMM-Newton
spectroscopy. We show that the absorption is most likely due to a dense ionised
wind driven by the QSO. This wind could be the mechanism by which the QSO
terminates the star formation in the host galaxy, and ends the supply of
accretion material, to produce the present day black hole/spheroid mass ratio.Comment: 4 pages, to appear in conference proceedings "Studying Galaxy
Evolution with Spitzer and Herschel
XMM-Newton observations of the Seyfert 1 AGN H0557-385
We present XMM-Newton observations of the Seyfert 1 AGN H0557-385. We have
conducted a study into the warm absorber present in this source, and using
high-resolution RGS data we find that the absorption can be characterised by
two phases: a phase with log ionisation parameter xi of 0.50 (where xi is in
units of ergs cm/s) and a column of 0.2e21 cm^-2, and a phase with log xi of
1.62 and a column of 1.3e22 cm^-2. An iron K alpha line is detected. Neutral
absorption is also present in the source, and we discuss possible origins for
this. On the assumption that the ionised absorbers originate as an outflow from
the inner edge of the torus, we use a new method for finding the volume filling
factor. Both phases of H0557-385 have small volume filling factors (< 1%). We
also derive the volume filling factors for a sample of 23 AGN using this
assumption and for the absorbers with log xi > 0.7 we find reasonable agreement
with the filling factors obtained through the alternative method of equating
the momentum flow of the absorbers to the momentum loss of the radiation field.
By comparing the filling factors obtained by the two methods, we infer that
some absorbers with log xi < 0.7 occur at significantly larger distances from
the nucleus than the inner edge of the torus.Comment: Accepted for publication in MNRA
Submm-bright X-ray absorbed QSOs at z~2: insights into the co-evolution of AGN and star-formation
We have assembled a sample of 5 X-ray-absorbed and submm-luminous type 1 QSOs
at which are simultaneously growing their central black holes
through accretion and forming stars copiously. We present here the analysis of
their rest-frame UV to submm Spectral Energy Distributions (SEDs), including
new Herschel data. Both AGN (direct and reprocessed) and Star Formation (SF)
emission are needed to model their SEDs. From the SEDs and their UV-optical
spectra we have estimated the masses of their black holes , their intrinsic AGN bolometric luminosities
, Eddington ratios
and bolometric corrections
. These values are common among optically and
X-ray-selected type 1 QSOs (except for RX~J1249), except for the bolometric
corrections, which are higher. These objects show very high far-infrared
luminosities (2 - 8) and Star Formation
Rates SFRy. From their and the shape of their
FIR-submm emission we have estimated star-forming dust masses of . We have found evidence of a tentative correlation between the
gas column densities of the ionized absorbers detected in X-ray (N)
and . Our computed black hole masses are amongst the most massive known.Comment: Accepted for publication in MNRAS, December 22, 2014, 17 pages, 5
figure
- …